The present invention relates to a transducer and apparatus for deep heat therapy in the treatment of musculoskeletal disorders, and more particularly to a low leakage radio frequency (RF) contact applicator design with skin and subcutaneous cooling, methods of applicator manufacturing, including applicator testing for quality assurance, as well as methods for detection of therapeutic response to achieve treatment control that may use the same transducer simultaneously for effector and sensor functions. Improved electronics for the apparatus and new radome and bolus designs are also disclosed.